c++11 Variadic Printf performance

Question

variadic template is introduced in c++11. And I found the printf function can be replaced using it. However, cout is used in the implementation. I am wondering if it is poss

Answer 1

At GoingNative2012, Andrei Alexandrescu gave an implementation of a variadic safe_printf(). He uses a two-step approach. First, check the format specifiers; and second, normalize the arguments being passed. Because the implementation delegates to printf() with checked formatters and arguments, there is no std::cout in sight and hardly any runtime overhead (the exception path should not be taken often in regular code)

Code summary:

template 
int safe_printf(const char * f, const Ts&... ts) 
{
    check_printf(f, normalizeArg(ts)...);  // check format specifiers
    return printf(f, normalizeArg(ts)...); // output with clean arguments
}

void check_printf(const char * f) 
{
    // checking is O(N) in length of format specifiers
    for (; *f; ++f) {
        if (*f != ’%’ || *++f == ’%’) continue;
        throw Exc("Bad format");
    }
}

// variadic check_print(const char*, T...) omitted, see slides

template 
typename enable_if::value, long>::type
normalizeArg(T arg) 
{ 
    return arg; 
}

// more overloads for float, T* and std::string omitted, see slides